Liquid crystal display

ABSTRACT

A single color liquid crystal display device is made up of a TN liquid crystal cell  7  with about 90° twisted nematic liquid crystals sealed in-between a pair of transparent substrates  1, 2  having respective transparent electrodes  3, 4,  a first polarizing film  17  disposed on the visible side of the TN liquid crystal cell  7,  and a second polarizing film  18 , a retardation film  6  for circularly polarized light, a cholestric liquid crystal polymer sheet  10,  a translucent light absorbing member  15  and a backlight  16  disposed successively on a side of the TN liquid crystal cell  7,  opposite from the visible side thereof. With such a constitution, display is rendered visible even at night by lighting up the backlight  16,  and colored display in a metallic tone can be indicated.

TECHNICAL FIELD

The invention relates to a liquid crystal display device, andparticularly, to a single color liquid crystal display device forcoloring its background and display parts.

BACKGROUND TECHNOLOGY

As for the single color liquid crystal display device for coloring itsbackground and display parts, several types have been proposed in thepast.

A first type is a single color liquid crystal display device made up byproviding a color polarizing film on the outer side of a liquid crystalcell thereof. This type has generally been in widespread use due to itssimple constitution.

A second type is a single color liquid crystal display device wherein adichroic pigment is mixed in nematic liquid crystals sealed in a liquidcrystal cell thereof, and the dichroic pigment is caused to movetogether with the nematic liquid crystals by the action of nematicliquid crystal molecules, and this type is called a guest-host LCD.

However, with any of these conventional-type single-color liquid crystaldisplay devices, colored characters and colored graphics produced by adye or the dichroic pigment are displayed against a background in white,or white characters and white graphics are displayed against abackground color produced by the dye or the dichroic pigment.Consequently, contrast declines. Furthermore, since the numbers ofavailable dyes and dichroic pigments are limited, there is also aproblem that the number of colors in which such liquid crystal displaydevices as described above can indicate display.

Accordingly, there has been proposed a third type of single color liquidcrystal display device comprising a polarizing film, a 90° twistednematic (TN) liquid crystal cell, a retardation film for circularlypolarizing film (a quarter-wavelength plate, ¼λ plate), a cholestricliquid crystal polymer sheet, and a light absorbing member.

Referring to FIG. 13, the display principle of the single color liquidcrystal display device of this type is described hereinafter.

Shown in FIG. 13, the single color liquid crystal display device is madeup of a polarizing film 8, a twist-aligned 90° TN liquid crystal cellwhich is not shown, a retardation film 9 for circularly polarized light,a cholestric liquid crystal polymer sheet 10, and a light absorbingmember 11.

In the left-hand part of the figure, an OFF-state indicating coloreddisplay is shown, wherein the polarizing film 8 and the retardation film9 for circularly polarized light are disposed such that the transmissionaxis 8 b of the polarizing film 8 is inclined 45° clockwise toward thephase delay axis 9 a of the retardation film 9 for circularly polarizedlight. As a result, linearly polarized light transmitted through thepolarizing film 8 is turned into right-handed circularly polarized lightafter passing through the retardation film 9 for circularly polarizedlight.

In the cholestric liquid crystal polymer sheet 10, a twist direction 10a is right handed, and a twist pitch is close to a natural lightwavelength, and accordingly, upon the right-handed circularly polarizedlight falling on the cholestric liquid crystal polymer sheet 10, lightcomponents in a scattering band width Δλ around a scattering centerwavelength λc are reflected due to the selective scattering phenomenon.Transmitted light composed of light components in wavelength regions,other than the scattering band width Δλ, is absorbed by the lightabsorbing member 11 made of a black paper or a black plastic sheet,whereupon a bright reflected color can be obtained.

If one defines n as the refractive index of a cholestric liquid crystalpolymer, and P as the twist pitch of the cholestric liquid crystalpolymer, the scattering center wavelength λc is given by the followingformula:

λc=n×P

Hence, the cholestric liquid crystal polymer sheet 10 having variousreflected colors can be obtained by adjusting the twist pitch P of thecholestric liquid crystal polymer.

Meanwhile, in the right-hand part of FIG. 13, an ON-state indicatingblack display is shown, wherein the polarizing film 8 and theretardation film 9 for circularly polarized light are disposed such thatthe transmission axis 8 a of the polarizing film 8 is inclined 45°counterclockwise toward the phase delay axis 9 a of the retardation film9 for circularly polarized light by rotating the transmission axis 8 aof the polarizing film 8 through 90°, so that linearly polarized lightafter passing through the retardation film 9 for circularly polarizedlight is turned into left-handed circularly polarized light.

Accordingly, even if the left-handed circularly polarized light falls onthe cholestric liquid crystal polymer sheet 10 having the twistdirection 10 a which is right handed, the selective scatteringphenomenon does not occur. As a result, all components of theleft-handed circularly polarized light are transmitted through thecholestric liquid crystal polymer sheet 10, and absorbed by the lightabsorbing member 11, thus indicating black display.

If a 90° TN liquid crystal cell is installed between the polarizing film8 and the retardation film 9 for circularly polarized light instead ofrotating the transmission axis 8 a of the polarizing film 8, this makesit possible to change by about 90° the polarization direction oflinearly polarized light falling on the retardation film 9 forcircularly polarized light depending on whether or not a voltage isapplied to the TN liquid crystal cell, so that a background part in theOFF-state and display parts in the ON-state can be controlledoptionally. Consequently, a single color liquid crystal display devicehaving such a constitution is able to display black characters against acolored background in a bright metallic tone.

Such related art as described above has been disclosed in JapanesePatent Laid-Open No. S52-5550 and Japanese Patent Laid-Open No.H6-230362. There has also been disclosed in, for example, JapanesePatent Laid-Open No. H6-230371, a similar liquid crystal display devicecomprising a first polarizing film, a TN liquid crystal cell, a secondpolarizing film, a retardation film for circularly polarized light, acholestric liquid crystal polymer sheet, and a light absorbing member,wherein the second polarizing film is installed between the TN liquidcrystal cell and the retardation film for circularly polarized light.

However, with these single color liquid crystal display devices usingthe cholestric liquid crystal polymer sheet, illumination bybacklighting is not feasible because of use of an opaque light absorbingmember made of a black paper, a black plastic sheet, or so forth, thuscausing a problem that display can not be shown in a dark environmentsuch as at night, and so forth.

DISCLOSURE OF THE INVENTION

The invention has been developed to solve the problem described above,and it is therefore an object of the invention to provide a single colorliquid crystal display device capable of rendering display visible evenin a dark environment such as at night, and so forth, so that charactersand graphics in a bright color can be displayed against a blackbackground, or conversely, characters and graphics in a black color canbe displayed in a colored background, using a backlight.

To this end, a liquid crystal display device according to the inventioncomprises a TN liquid crystal cell with about 90° twisted nematic liquidcrystals sealed in-between a pair of transparent substrates havingrespective electrodes, a first polarizing film disposed on the visibleside of the TN liquid crystal cell, and a second polarizing film, aretardation film for circularly polarized light, a cholestric liquidcrystal polymer sheet, a translucent light absorbing member, and abacklight disposed successively on a side of the TN liquid crystal cell,opposite from the visible side thereof.

In place of the TN liquid crystal cell described above, an STN liquidcrystal cell with 180° to 270° twisted nematic liquid crystalssandwiched between a pair of transparent substrates having respectiveelectrodes may be installed, a retardation film may be disposed on thevisible side of the STN liquid crystal cell, and a first polarizing filmmay be disposed on the outer side of the retardation film. Further, inplace of the retardation film, a twist retardation film may be disposed.

Furthermore, instead of installing the translucent light absorbingmember, a light emitting face of the backlight may be caused to have afunction of scattering polarized light, and the backlight may bedisposed opposite to the cholestric liquid crystal polymer sheet.

Otherwise, a liquid crystal display device according to the inventionmay comprise the TN liquid crystal cell, a first polarizing filmdisposed on the visible side of the TN liquid crystal cell, and a firstretardation film for circularly polarized light, a cholestric liquidcrystal polymer sheet, a second retardation film for circularlypolarized light, a second polarizing film, a translucent light absorbingmember, and a backlight disposed successively on a side of the TN liquidcrystal cell, opposite from the visible side thereof.

In this case as well, instead of installing the translucent lightabsorbing member, a light emitting face of the backlight may be causedto have a function of scattering polarized light, and the backlight maybe disposed opposite to the cholestric liquid crystal polymer sheet.

With any of the liquid crystal display devices described above, in placeof the TN liquid crystal cell, the STN liquid crystal cell may beinstalled, a retardation film may be disposed on the visible side of theSTN liquid crystal cell, and a first polarizing film may be disposed onthe outer side of the retardation film. Further, in place of theretardation film, a twisted retardation film may be disposed.

Further, a luminescence center wavelength of the backlight is preferablydeviated by not less than 50 nm from a selected scattering centerwavelength of the cholestric liquid crystal polymer sheet.

More preferably, the backlight has not less than two luminescence centerwavelengths, and at least one of the luminescence center wavelengths isdeviated by not less than 50 nm from a selective scattering centerwavelength of the cholestric liquid crystal polymer sheet.

Furthermore, a reflection-type polarizing film (a polarizing filmreflecting the light linearly polarized in the direction orthogonal tothe transmission axis thereof) may be disposed as the second polarizingfilm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing a constitution of a liquidcrystal display device according to a first embodiment of the invention;

FIG. 2 is a schematic illustration showing relative positions ofrespective components of the liquid crystal display device according tothe first embodiment of the invention;

FIG. 3 is a schematic sectional view showing a constitution of a liquidcrystal display device according to a second embodiment of theinvention;

FIG. 4 is a schematic illustration showing relative positions ofrespective components of the liquid crystal display device according tothe second embodiment of the invention;

FIG. 5 is a schematic sectional view showing a constitution of a liquidcrystal display device according to a third embodiment of the invention;

FIG. 6 is a schematic illustration showing relative positions ofrespective components of the liquid crystal display device according tothe third embodiment of the invention;

FIG. 7 is a schematic sectional view showing a constitution of a liquidcrystal display device according to a fourth embodiment of theinvention;

FIG. 8 is a schematic sectional view showing a constitution of a liquidcrystal display device according to a fifth embodiment of the invention;

FIG. 9 is a schematic sectional view showing a constitution of a liquidcrystal display device according to a sixth embodiment of the invention;

FIG. 10 is a schematic illustration showing relative positions ofrespective components of the liquid crystal display device according tothe sixth embodiment of the invention;

FIG. 11 is a diagrammatic view showing transmittance and emissionspectrum of a backlight, of the liquid crystal display device accordingthe first to sixth embodiments of the invention;

FIG. 12 is a diagrammatic view showing transmittance and emissionspectrum of a backlight, of a liquid crystal display device according toa seventh embodiment of the invention; and

FIG. 13 is a schematic perspective view illustrating the displayprinciple of a conventional single color liquid crystal display deviceusing a cholestric liquid crystal polymer sheet.

BEST MODE FOR CARRYING OUT THE INVENTION

A construction, operation and effect of a liquid crystal display deviceaccording to a preferred embodiment of the invention is now described indetail as follows with attached drawings.

First Embodiment: FIG. 1, FIG. 2 and FIG. 11

A construction of a liquid crystal display device according to a firstembodiment of the invention is now described with reference to FIGS. 1and 2.

FIG. 1 is a schematic sectional view of the liquid crystal displaydevice, and FIG. 2 is a view showing relative positions of respectiveelements thereof.

The liquid crystal display device according to the first embodimentcomprises, shown in FIG. 1, a first transparent substrate 1 made of aglass plate having a thickness of 0.7 mm on which first transparentelectrodes 3 made of indium tin oxide (hereinafter referred to as “ITO”)are provided, a second transparent substrate 2 made of a glass platehaving a thickness of 0.7 mm on which a second transparent electrodes 4made of ITO are provided, and a sealant 5 for laminating the pair ofsubstrates, wherein 90° twist-aligned nematic liquid crystals 6 aresealed in between the pair of transparent first and second substrates 1and 2, thereby forming a TN liquid crystal cell 7.

A first polarizing film 17 is disposed on a visible side (a side wherean observer sees, the upper side in FIG. 1) on the second substrate 2 ofthe TN liquid crystal cell 7, and a second polarizing film 18, aretardation film 9 for circularly polarized light, a cholesteric liquidcrystal polymer sheet 10, a translucent light absorbing member 15 and abacklight 16 are disposed successively on a side opposite from thevisible side, thereby constituting a liquid crystal display device 40.

The first substrate 1, the second polarizing film 18, the retardationfilm 9 for circularly polarized light and the cholesteric liquid crystalpolymer sheet 10 are bonded to one another by an acrylic adhesive (notshown). Further, the first polarizing film 17 and the second substrate 2are also bonded to each other by an acrylic adhesive (not shown).

Suppose the difference of birefringence Δn of the nematic liquidcrystals 6 used in the TN liquid crystal cell is 0.15, and a cell gap dbetween the first substrate 1 and the second substrate 2 is 8000 nm.Accordingly, the Δnd value of the TN liquid crystal cell 7 which is aproduct of the difference of birefringence Δn of the nematic liquidcrystals 6 and the cell gap d is 1200 nm. As the Δnd value decreases,the optical rotatory power lowers, and hence it is preferable that theΔnd value is not less than 500 nm.

An alignment layer (not shown) is formed, respectively, on an innersurface of the first transparent electrodes 3, and an inner surface ofthe second transparent electrodes 4. Accordingly, as shown in FIG. 2, analignment direction 7 a of lower liquid crystal molecules points 45°downward to the right when rubbing treatment in the direction of −45° onthe basis of the horizontal axis H is applied to the first substrate 1,while an alignment direction 7 b of upper liquid crystal moleculespoints 45° upward to the right when rubbing treatment in the directionof +45° on the basis of the horizontal axis H is applied to the secondsubstrate 2, thereby forming the left-handed twist-aligned 90° TN liquidcrystal cell 7.

The first polarizing film 17 is disposed such that the transmission axis17 a thereof points 45° upward to the right in the same manner as thealignment direction 7 b of upper liquid crystal molecules of the TNliquid crystal cell 7, while second polarizing film 18 is disposed suchthat the transmission axis 18 a thereof points 45° downward to the rightin the same manner as the alignment direction 7 a of lower liquidcrystal molecules of the TN liquid crystal cell 7.

The retardation film 9 for circularly polarized light is prepared byspreading a polycarbonate resin to a thickness of about 60 μm, and thephase difference value is 140 nm, and a phase delay axis 9 a thereof isoriented horizontally. The cholesteric liquid crystal polymer sheet 10is disposed underneath the retardation film 9 for circularly polarizedlight, while a film prepared by dying polyethylene terephthalate (PET)having a thickness of 20 μm with a black dye so that the transmittancebecomes 50% is installed as the translucent light absorbing member 15.

The cholesteric liquid crystal polymer sheet 10 is formed by applyingalignment treatment to a base film which is a triacetylcellulose (TAC)film of 80 μm thickness, applying cholesteric liquid crystal polymerthereon, adjusting at a high temperature showing a liquid crystal phaseso as to set the twist pitch to 380 nm and rotate clockwise with planeralignment in parallel with the base film, then cooling to not higherthan the glass-transition temperature for solidification. Accordingly,the twist central axis is perpendicular to the base frame.

An electroluminescence plate (hereinafter referred to as “EL plate”)having a thickness of 200 μm, and showing emitted light in a bluishgreen color used for the backlight 16. Even if the cholestric liquidcrystal polymer sheet 10, the translucent light absorbing member 15 andthe backlight 16 are disposed at whatever rotational angle withinrespective planes in parallel with each other, displaying characteristicwill not be affected, and therefore, in FIG. 2, illustration ofdisposition directions is omitted.

Next, operation of displaying color of the liquid crystal display deviceaccording to the first embodiment of the invention is describedhereinafter.

In the liquid crystal display device 40, the linearly polarized lightwhich falls on the liquid crystal display device from the visible sideand passed the first polarizing film 17 and is polarized in thedirection of the transmission axis 17 a in a state where no voltage isapplied to the first transparent electrodes 3 and the second transparentelectrodes 4 of the TN liquid crystal cell 7 falls on the TN liquidcrystal cell 7 in the alignment direction 7 b of upper liquid crystalmolecules, and is rotated by 90° by the TN liquid crystal cell 7 andoutgoes after it is turned into the linearly polarized light in thealignment direction 7 a of lower liquid crystal molecules. Since thesecond polarizing film 18 is disposed such that the alignment direction7 a of lower liquid crystal molecules and the transmission axis 18 a ofthe second polarizing film 18 are in parallel with each other, thelinearly polarized light falling on the second polarizing film 18 passesthe second polarizing film 18 as it is.

Accordingly, the polarized light falls on the retardation film 9 forcircularly polarized light while it is rotated clockwise by 45° from thephase delay axis 9 a. Accordingly, it is turned into right-handedcircularly polarized light in the same manner as the OFF-state shown inFIG. 13, which is the same as the twist direction 10 a of thecholesteric liquid crystal polymer sheet 10. Accordingly, when theright-handed circularly polarized light falls on the cholesteric liquidcrystal polymer sheet 10, light components in a scattering bandwidth Δλaround a scattering center wavelength λc are reflected due to theselective scattering phenomenon, and light components transmittedthrough wavelength regions, other than the scattering bandwidth Δλ, isabsorbed by the translucent light absorbing film 15, whereupon areflected color in a bright metallic tone can be obtained.

If one defines n as the refractive index of a cholestric liquid crystalpolymer, and P as the twist pitch of the cholestric liquid crystalpolymer, the scattering center wavelength λc is given by the followingformula: λc=n×P Since right-twisted cholesteric liquid crystal polymerhaving n as 1.65, P as 370 nm is employed in this embodiment, thescattering center wavelength λc becomes 610 nm, thereby obtaining agolden reflected color in a metallic tone.

Now, when a voltage is applied between the first transparent electrodes3 of the TN liquid crystal cell 7 and the second transparent electrodes4 of the same, molecules of the nematic liquid crystals 6 are caused torise up, the light rotation property is extinguished. Then, linearlypolarized light polarized in the alignment direction 7 b of upper liquidcrystal molecules falls on the TN liquid crystal cell 7, it passed as itis. Accordingly, the linearly polarized light falling on the secondpolarizing film 18 after passing the TN liquid crystal cell 7 ispolarized in the direction intersecting the transmission axis 18 athereof at right angles, so that all components of light falling on thesecond polarizing film 18 are absorbed thereby, indicating blackdisplay.

In FIG. 11, the transmittance of the cholesteric liquid crystal polymersheet 10 adopted in the first embodiment at the selective scatteringstate (no voltage is applied between the first transparent electrodes 3and the second transparent electrodes 4) is shown by a solid curve 53,whereas the transmittance of the same when indicating black display (avoltage is applied between the first transparent electrodes 3 and thesecond transparent electrodes 4) is shown by a solid curve 52. At theselective scattering state, it is found from the curve 53 thatright-handed circularly polarized light in the range from 560 nm to 670nm around the scattering center wavelength of λc=610 nm is reflected,but light out of the scattering bandwidth transmits as it is.Accordingly, if the transmitted light is restrained from returning tothe visible side by absorbing that by the translucent light absorbingfilm 15, thereby a bright golden color can be performed by the reflectedlight due to the selective scattering phenomenon. When indicating ablack display, as shown by the curve 52, light transmitted through thefirst polarizing film 17 are almost absorbed by the second polarizingfilm 18, thereby indicating a black display.

Next, operation of the backlight 16 in FIG. 1 is described hereinafter.A dotted line curve 54 in FIG. 11 is a spectrum showing relative lightemitting density of the EL plate showing emitted light in a bluish greencolor used for the backlight 16 of the liquid crystal display device 40,which indicates emitted light in a bluish green color in a luminescencecenter wavelength λL=510 nm.

With the liquid crystal display device 40, light does not transmit in anON-state indicating a black display when a voltage is applied as shownin the curve 52, so that it remains dark even if the backlight 16 is litup. However, golden reflected color is indicated in a state where novoltage is applied, and light having not more than 560 nm can transmitas shown in the curve 53.

Light emitted by the backlight 16 having luminescence center wavelengthλL=510 nm that is smaller than the selective scattering centerwavelength λc=610 nm of the cholesteric liquid crystal polymer sheet 10by 100 nm substantially completely transmits through the cholestericliquid crystal polymer sheet 10, thereby illuminating brightly, so thatan excellent visibility can be obtained even at night.

If the translucent light absorbing member 15 and the backlight 16 areprovided without installing the second polarizing film 18 in FIG. 1, theliquid crystal display device capable of indicating single color in ametallic tone can be obtained. In this case, the operation of displayingcolor is the same as that in the first embodiment in the case ofOFF-state indicating a golden display, but in the case of ON-stateindicating a black display light outgoing from the retardation film 9for circularly polarized light is turned into left-handed state ofcircularly polarized light, and it transmits through the right-twistedcholesteric liquid crystal polymer sheet 10 so that it is absorbed bythe translucent light absorbing member 15 to indicate a black color.

If the backlight 16 is lit up in this state, light transmitted throughthe translucent light absorbing member 15 illuminates bright because thetransmittance in the black display part in the ON-state is high, whilelight illuminates dark because the transmittance in golden part in theOFF-state is low, thereby indicating an inversion display in monochromerelation contrary to the reflected state using an external light. Inthis case, the difference in an amount of transmittance of a backlightbetween ON-state and OFF-state is small, thereby lowering a contrast.

Further, if the backlight 16 of the liquid crystal display device 40 islit up in a dim environment, the golden portion in the OFF displayreflects the external light and illuminates, while the black portion inthe ON state transmits the backlight therethrough and illuminates, sothat the contrast between the characters and a background scarcelypresents, thereby markedly lowering the visibility.

However, with the liquid crystal display device 40, it is the samedisplay in a monochrome relation viewing in a reflected state using anexternal light and viewing in a transmittance state using a backlight,thereby improving the visibility when lighting up the backlight in a dimenvironment.

With the construction comprising the first polarizing film 17, the TNliquid crystal cell 7, the second polarizing film 18, the retardationfilm 9 for circularly polarized light, the cholesteric liquid crystalpolymer sheet 10, the translucent light absorbing member 15 and thebacklight 16, a display of bright reflected color with high contrast isobtained, and also it becomes a correct conversion even by illuminationby backlighting, thereby obtaining the liquid crystal display devicecapable of indicating a single colored display in a metallic tone and ofenhancing visibility even at night.

Modification of First Embodiment

In the foregoing first embodiment, the selective scattering centerwavelength λc of the cholesteric liquid crystal polymer sheet 10 and theluminescence center wavelength λL of the backlight are deviated by 100nm, but if they are deviated by 50 nm, the brightness of illumination ofthe backlight is somewhat lowered, which however does not cause anyproblem.

Although the cholesteric liquid crystal polymer having a pitch P=370 nmis used as the cholesteric liquid crystal polymer sheet 10 to form theliquid crystal display device indicating golden and black displays inthe first embodiment, it is possible to change a color tone in areflecting state by optionally changing a pitch P of the cholestericliquid crystal polymer. For example, it is possible to obtain a liquidcrystal display device indicating blue and black displays supposing thatP=300 nm (λc=490 nm). In this case, an EL plate having a luminescencecenter wavelength λL of 560 nm, and showing emitted light in an orangecolor is employed.

Although the an EL plate showing emitted light in a bluish green coloris employed as the backlight 16 in the first embodiment, even if a sidelight consisting of a light emitting diode (LED) showing emitted lightin a green color which is attached to a plastic light guide plate isemployed, the bright illumination which is the same as the foregoing canbe obtained.

Further, although the first embodiment indicates a colored display in astate where no voltage is applied and a black display in a state where avoltage is applied, if the transmission axis 17 a of the firstpolarizing film 17 is rotated by 90° to be oriented in the samedirection as the alignment direction 7 a of lower liquid crystalmolecule, it is possible to indicate a black display in a state where novoltage is applied and indicate a colored display in a state where avoltage is applied.

Alternatively, even if the transmission axis 18 a of the secondpolarizing film 18 is rotated by 90°, it is possible to indicate a blackdisplay in a state where no voltage is applied and a colored display ina state where a voltage is applied.

Although the retardation film 9 for circularly polarized light isdisposed between the second polarizing film 18 and the cholestericliquid crystal polymer sheet 10 in the first embodiment, the retardationfilm 9 for circularly polarized light can be removed although thereflecting efficiency of the cholesteric liquid crystal polymer sheet 10is somewhat lowered, and a metallic color becomes somewhat dark.

Second Embodiment: FIGS. 3 and 4

A liquid crystal display device according to a second embodiment of theinvention is now described with reference to FIGS. 3 and 4.

The liquid crystal display device of this embodiment is the same as thefirst embodiment in construction except that 225° twist-aligned STNliquid crystal cell as the liquid crystal cell, and that a retardationfilm are used.

FIGS. 3 and 4 are views for explaining the construction of the liquidcrystal display device of the second embodiment which are the same asFIGS. 1 and 2, wherein the components which correspond to those in FIGS.1 and 2 are denoted by the same reference numerals and the explanationthereof is omitted.

The liquid crystal display device 40 according to the second embodimentcomprises a first transparent substrate 1 made of a glass plate having athickness of 0.7 mm on which a first transparent electrodes 3 made ofITO are provided, a second transparent substrate 2 made of a glass platehaving a thickness of 0.7 mm on which second transparent electrodes 4made of ITO are provided, and a sealant 5 for laminating the pair ofsubstrates 1 and 2 wherein 225° twist-aligned nematic liquid crystals 6are sealed in between the pair of transparent first and secondsubstrates 1 and 2, thereby forming a STN liquid crystal cell 12.

A retardation film 13 and a first polarizing film 17 are disposedsuccessively outside the second substrate 2 at a visible side of the STNliquid crystal cell 12, and a second polarizing film 18, a retardationfilm 9 for circularly polarized light, a cholesteric liquid crystalpolymer sheet 10, a translucent light absorbing member 15 and abacklight 16 are disposed successively on a side opposite from thevisible side, thereby constituting a liquid crystal display device 40.

The first polarizing film 17, the second polarizing film 18, thecholesteric liquid crystal polymer sheet 10, the retardation film 9 forcircularly polarized light, the translucent light absorbing member 15and the backlight 16 are the same as those employed in the firstembodiment.

A first substrate 1, the second polarizing film 18, the retardation film9 for circularly polarized light and the cholesteric liquid crystalpolymer sheet 10 are respectively bonded using an acrylic adhesive (notshown). Further, the first polarizing film 17, the retardation film 13and a second substrate 2 are also bonded using an acrylic adhesive (notshown).

Suppose the difference of birefringence Δn of the nematic liquidcrystals 6 to be used is 0.15 and a cell gap d between the firstsubstrate 1 and the second substrate 2 is 5400 nm. Accordingly, the Δndvalue of the liquid crystal cell which is a product of the difference ofthe birefringence Δn of the nematic liquid crystals 6 and the cell gap dis 810 nm. Further, a twist pitch of the nematic liquid crystals 6 isadjusted to 1100 nm.

An alignment layer (not shown) is formed, respectively, on an innersurface of the first transparent electrodes 3, and an inner surface ofthe second transparent electrodes 4, and shown in FIG. 4, an alignmentdirection 12 a of lower liquid crystal molecules points 22.5° upward tothe right when rubbing treatment in the direction of +22.5° on the basisof the horizontal axis H is applied to the first substrate 1, while analignment direction 12 b of upper liquid crystal molecules points 22.5°downward to the right when rubbing treatment in the direction of −22.5°on the basis of the horizontal axis H is applied to the second substrate2, thereby forming the left-handed 225° twist-aligned STN liquid crystalcell 12.

The first polarizing film 17 is disposed such that the transmission axis17 a thereof is oriented in the direction of −70° on the basis of thehorizontal axis H, and the retardation film 13 made of polycarbonateresin and having the thickness of 50 μm and phase difference value of550 nm is disposed between the STN liquid crystal cell 12 and the firstpolarizing film 17 such that a phase delay axis 13 a thereof is orientedin the direction of 60° on the basis of the horizontal axis H.

The second polarizing film 18 is disposed underneath the STN liquidcrystal cell 12 such that the transmission axis 18 a thereof is orientedin the direction of −15° on the basis of the horizontal axis H, and theretardation film 9 for circularity polarized light is disposed such thatthe phase delay axis 9 a thereof is oriented in the direction of 30° onthe basis of the horizontal axis H so that the phase delay axis 9 aforms an angle of 45° with the transmission axis 18 a of the secondpolarizing film 18.

To improve viewing angles characteristic, the retardation film 13 uses abiaxial retardation film satisfying the relation of nx>nz>ny supposingthat nx is the refractive index in the phase delay direction, ny isrefractive index in the direction of Y axis and nz is the refractiveindex in the thickness direction. It is needless to say that the use ofan uniaxial retardation film causes no problem.

Even if the cholestric liquid crystal polymer sheet 10, the translucentlight absorbing member 15 and the backlight 16 are disposed at whateverrotational angle within respective planes in parallel with each other,displaying characteristic will not be affected, and therefore, in FIG.4, illustration of disposition directions is omitted.

Next, operation of displaying color of the liquid crystal display device40 according to the second embodiment of the invention is describedhereinafter. With the liquid crystal display device 40, in a state whereno voltage is applied to the STN liquid crystal cell 12, linearlypolarized light falling thereon from the visible side thereof (upperside in FIG. 3) through the first polarizing film 17 and polarized inthe direction of the transmission axis 17 a of the first polarizing film17, is turned into a state of elliptic polarized light after transmittedthrough the STN liquid crystal cell 12 in the case where the retardationfilm 13 is not installed, so that circularly polarized light can not beproduced even after passing through the retardation film 9 forcircularly polarized light, thereby indicating insufficient display.

However, since the retardation film 13 is installed between the firstpolarizing film 17 and the STN liquid crystal cell 12, the linearlypolarized light falling on the retardation film 13 through the firstpolarizing film 17 is turned into a state of elliptic polarized light.The elliptic polarized light is corrected during passage through the STNliquid crystal cell 12, is turned into the substantially linearlypolarized light, then it is turned into the linearly polarized lightwhich is at about a 55° counterclockwise angle with respect to thetransmission axis 17 a of the first polarizing film 17, and outgoes.

Since the second polarizing film 18 is disposed such that thetransmission axis 18 a of the second polarizing film 18 is oriented inthe direction at −15° on the basis of the horizontal axis H, thelinearly polarized light falling thereon from the first polarizing film17 is transmitted through the second polarizing film 18 as it is. Sincethe retardation film 9 for circularly polarized light is disposed suchthat the phase delay axis 9 a thereof is oriented in the direction of+45° with respect to the transmission axis 18 a of the second polarizingfilm, and linearly polarized light at a 45° clockwise angle with respectto the phase delay axis 9 a of the retardation film 9 for circularlypolarized light falls thereon, it is turned into right-handed circularlypolarized light.

As with the case of the first embodiment, the cholestric liquid crystalpolymer sheet 10 which is right-handed is employed, consequently, lightcomponent in a scattering bandwidth Δλ around a scattering centerwavelength birefringence λc are reflected due to the selectivescattering phenomenon, and light components transmitted throughwavelength regions, other than the scattering bandwidth Δλ, is absorbedby the translucent light absorbing member 15, whereupon a goldenreflected color in a bright metallic tone can be obtained.

Now, when a voltage is applied between the first transparent electrodes3 of the STN liquid crystal cell 12 and the second transparentelectrodes 4 of the same, molecules of the nematic liquid crystals 6 arecaused to rise up, and birefringency of the STN liquid crystal cell 12undergoes a change, so that polarization of linearly polarized lightoutgoing is rotated by about 90° to be in the direction at +75° on thebasis of the horizontal axis H shown in FIG. 4. Accordingly, polarizingdirection of the linearly polarized light transmitted through the STNliquid crystal cell 12 is deviated by 90° from the transmission axis 18a of the second polarizing film 18, so that all components of lightfalling on the second polarizing film 18 are absorbed thereby,indicating black display. Accordingly, it is possible to indicate ablack display with high contrast by the use of the second polarizingfilm 18.

As with the case of the first embodiment, an EL plate having aluminescent center wavelength λL=510 nm, and showing emitted light in abluish green color is used for the backlight 16. In a black displaystate where a voltage is applied, light is not transmitted through theliquid crystal display device, however, in a sate where no voltage isapplied and display in a golden reflected color is indicated, lightcomponents having wavelengths not more than 560 nm can be transmittedtherethrough.

Accordingly, light emitted by the backlight 16 having luminescencecenter wavelength λL that is smaller than the selected scattering centerwavelength λc=610 nm of the cholesteric liquid crystal polymer sheet 10by 100 nm substantially completely transmits, thereby illuminatingbrightly. Further, so it indicates the same display in brightnessrelation as the display by an external light without backlighting,enhance visibility can be performed even at night.

With the construction comprising the first polarizing film 17, theretardation film 13, the STN liquid crystal cell 12, the secondpolarizing film 18, the retardation film 9 for circularly polarizedlight, the cholesteric liquid crystal polymer sheet 10, the translucentlight absorbing member 15, and the backlight 16, a display of brightreflected color with high contrast is obtained, and it also becomes acorrect conversion even by illumination by backlighting, therebyobtaining the liquid crystal display device capable of indicating asingle colored display in a metallic tone and of enhancing visibilityeven at night.

Modification of Second Embodiment

Although the 225° twist-aligned STN liquid crystal cell was employed asthe STN liquid crystal cell 12 in the second embodiment, the liquidcrystal display device which is the same as that in the secondembodiment can be obtained even if a 180° to 270° twist-aligned STNliquid crystal cell is employed.

Although one piece of retardation film 13 is employed for returning thestate of elliptical polarized light of the STN liquid crystal cell 12 tothe linearly polarized light in the second embodiment, if plural piecesof retardation films are employed, the state of elliptical polarizedlight can be returned to a more complete linearly polarized light,thereby indicating a more excellent black display and a colored display.The plural pieces of retardation films may be installed on one side ofthe STN liquid crystal cell 12, or they may be divided and installed onboth sides of the STN liquid crystal cell 12.

Further, although the retardation film 9 for circularly polarized lightis installed between the second polarizing film 18 and the cholestericliquid crystal polymer sheet 10 in the second embodiment, even if theretardation film 9 for circularly polarized light is omitted, the liquidcrystal display device can be practicably used, though the reflectingefficiency of the cholesteric liquid crystal polymer sheet 10 issomewhat lowered and metallic color becomes somewhat dark.

Third Embodiment: FIGS. 5 and 6

A liquid crystal display device according to a third embodiment of theinvention is now described with reference to FIGS. 5 and 6.

Since the liquid crystal display device of this embodiment is the sameas the first embodiment in construction except that 240° twist-alignedSTN liquid crystal cell as the liquid crystal cell is used, and that atwisted retardation film is installed.

FIGS. 5 and 6 are views for explaining the construction of the liquidcrystal display device of the third embodiment which are the same asFIGS. 1 and 2, wherein the components which correspond to those in FIGS.1 and 2 are denoted by the same reference numerals and the explanationthereof is omitted.

The liquid crystal display device 40 according to the third embodimentcomprises a first transparent substrate 1 made of a glass plate having athickness of 0.7 mm on which first transparent electrodes 3 made of ITOare provided, a second transparent substrate 2 made of a glass platehaving a thickness of 0.7 mm on which second transparent electrodes 4made of ITO are provided, and a sealant 5 for laminating the pair ofsubstrates 1 and 2 wherein 240° twist-aligned nematic liquid crystals 6are sealed in between the pair of transparent first and secondsubstrates 1 and 2, thereby forming a STN liquid crystal cell 14.

A twisted retardation film 19 and a first polarizing film 17 areinstalled successively outside the second substrate 2 at a visible sideof the STN liquid crystal cell 14, and a second polarizing film 18, aretardation film 9 for circularly polarized light, a cholesteric liquidcrystal polymer sheet 10, a translucent light absorbing member 15 and abacklight 16 are disposed successively on a side opposite from thevisible side, thereby constituting a liquid crystal display device 40.

The first polarizing film 17, the second polarizing film 18, thecholesteric liquid crystal polymer sheet 10, and the retardation film 9for circularly polarized light, the translucent light absorbing member15 and the backlight 16 are the same as those employed in the firstembodiment.

A first substrate 1, the second polarizing film 18, the retardation film9 for circularly polarized light and the cholesteric liquid crystalpolymer sheet 10 are respectively bonded using an acrylic adhesive (notshown). Further, the first polarizing film 17, the twisted retardationfilm 19 and a second substrate 2 are also bonded using an acrylicadhesive (not shown).

Suppose the difference Δn of birefringence of the nematic liquidcrystals 6 used in the STN liquid crystal cell 14 is 0.15, and a cellgap d between the first substrate 1 and the second substrate 2 is 5600nm. Accordingly, the Δnd value of the liquid crystal cell which is aproduct of the difference of birefringence Δn of the nematic liquidcrystals 6 and the cell gap d is 840 nm. Further, the twist pitch of thenematic liquid crystals 6 is adjusted to 1100 nm.

An alignment layer (not shown) is formed, respectively, on an innersurface of the first transparent electrodes 3, and an inner surface ofthe second transparent electrodes 4, facing each other, and shown inFIG. 6, an alignment direction 14 a of lower liquid crystal moleculespoints 30° upward to the right when rubbing treatment in the directionof +30° on the basis of the horizontal axis H is applied to the firstsubstrate 1, while an alignment direction 14 b of upper liquid crystalmolecules points 30° downward to the right when rubbing treatment in thedirection of −30° on the basis of the horizontal axis H is applied tothe second substrate 2, thereby forming the left-handed 240° STN liquidcrystal cell 14.

The first polarizing film 17 is disposed such that the transmission axis17 a thereof is oriented in the direction of −45° on the basis of thehorizontal axis H and the twisted retardation film 19 having Δnd valueof 610 nm and 220° twisted clockwise is disposed between the STN liquidcrystal cell 14 and the first polarizing film 17 so as to be oriented inthe direction of +55° on the basis of the horizontal axis H such that alower molecule axis 19 a thereof intersects the alignment direction 14 bof the upper liquid crystal molecules substantially at right angles.Accordingly, an upper molecule axis 19 b of the twisted retardation film19 comes to be oriented in the direction of −85°.

The second polarizing film 18 is disposed underneath the first substrate1 such that the transmission axis 18 a thereof is oriented in thedirection of +85° on the basis of the horizontal axis H, and theretardation film 9 for circularity polarized light is disposed such thatthe phase delay axis 9 a thereof is oriented in the direction of −50° onthe basis of the horizontal axis H so that the phase delay axis 9 aforms an angle of 45° with the transmission axis 18 a of the secondpolarizing film 18.

The twisted retardation film 19 is formed by applying alignmenttreatment to a base film which is a triacetylcellulose (TAC) film of 80μm thickness, applying liquid crystal polymer thereon, adjustingthickness and twist pitch thereof at a high temperature showing a liquidcrystal phase so as to have a twist angle of 220°, then cooling to nothigher than the glass-transition temperature for solidification.

Even if the cholestric liquid crystal polymer sheet 10, the translucentlight absorbing member 15, and the backlight 16 are disposed at whateverrotational angle within respective planes in parallel with each other,displaying characteristic will not be affected, and therefore, in FIG.6, illustration of disposition directions is omitted.

Next, operation of displaying color with the third embodiment of theliquid crystal display device according to the invention is describedhereinafter.

With the liquid crystal display device 40, in a state where no voltageis applied to the STN liquid crystal cell 14, linearly polarized lightfalling thereon from the visible side thereof through the firstpolarizing film 17 is polarized in the direction of the transmissionaxis 17 a of the first polarizing film 17, and is turned into a state ofelliptic polarized light after transmitted through the STN liquidcrystal cell 14 in the case where the twisted retardation film 19 is notinstalled, so that circularly polarized light can not produced evenafter passing through the retardation film 9 for circularly polarizedlight, thereby indicating insufficient display.

However, since the twisted retardation film 19 is installed between thefirst polarizing film 17 and the STN liquid crystal cell 14, thelinearly polarized light falling on the twist retardation film 19 fromthe first polarizing film 17 is turned into a state of ellipticpolarized light. The elliptic polarized light is corrected duringpassage through the STN liquid crystal cell 14, is turned intosubstantially linearly polarized light, and is rotated clockwise byabout 50° with respect to the transmission axis 17 a of the firstpolarizing film 17, and outgoes in the direction of polarization at 85°on the basis of the horizontal axis H shown in FIG. 6.

Since the second polarizing film 18 is disposed such that thetransmission axis 18 a thereof is oriented in the direction at 85° onthe basis of the horizontal axis H, the linearly polarized light fallingthereon from the first polarizing film 17 is transmitted through thesecond polarizing film 18 as it is. Since the retardation film 9 forcircularly polarized light is disposed such that the phase delay axis 9a thereof is oriented in the direction of +45° with respect to thesecond polarizing film 18, linearly polarized light at a 45° clockwiseangle with respect to phase delay axis of the retardation film 9 forcircularly polarized light falls thereon, and is turned intoright-handed circularly polarized light.

As with the case of the first embodiment, the cholestric liquid crystalpolymer sheet 10 which is right handed is absorbed, consequently, lightcomponents in a scattering bandwidth Δλ around a scattering centerwavelength λc are reflected due to the selective scattering phenomenon,and light components transmitted through wavelength regions other thanthe scattering bandwidth Δλ, is absorbed by the translucent lightabsorbing member 15, whereupon a golden reflected color in a brightmetallic tone can be obtained.

Now, when a voltage is applied between the first transparent electrodes3 of the STN liquid crystal cell 14 and the second transparentelectrodes 4 of the same, molecules of the nematic liquid crystals 6 arecaused to rise up, and birefringency of the STN liquid crystal cell 14undergoes a change, so that polarization direction of linearly polarizedlight outgoing is rotated by about 90° so as to be in the direction at−5° on the basis of the horizontal axis H. Accordingly, the linearlypolarized light transmitted through the STN liquid crystal cell 14 isdeviated by 90° from the transmission axis 18 a of the second polarizingfilm 18, so that all components of light falling on the secondpolarizing film 18 are absorbed thereby, indicating black display.

Further, as a result of using the twisted retardation film 19 in placeof the retardation film 13 used in the second embodiment, ellipticpolarized light can be fully corrected, and linear polarizationcharacteristics of light transmitted through the STN liquid crystal cell14 is enhanced, so that display that is brighter and higher contrastthan that in the case of the liquid crystal display device using theretardation film 13 can be obtained.

As with the case of the first embodiment, an EL plate having aluminescent center wavelength λL=510 nm, and showing emitted light in abluish green color used for the backlight. In a black display statewhere a voltage is applied, light is not transmitted through the liquidcrystal display device 40, however, in a sate where no voltage isapplied and display in a golden reflected color is indicated, lightcomponents having wavelengths not more than 560 nm can be transmittedtherethrough.

Accordingly, light emitted by the backlight 16 having luminescencecenter wavelength λL that is smaller than the selected scattering centerwavelength λc=610 nm of the cholesteric liquid crystal polymer sheet 10by 100 nm completely transmits, thereby illuminating brightly. Further,it becomes a correct conversion which is the same as the display by anexternal light when the backlight 16 is not lit up, so that an excellentvisibility can be obtained even at night.

With the construction comprising the first polarizing film 17, thetwisted retardation film 19, the second polarizing film 18, theretardation film 9 for circularly polarized light, the cholestericliquid crystal polymer sheet 10, the translucent light absorbing member15, and the backlight 16, it is possible to obtain a liquid crystaldisplay device capable of indicating a bright reflected colored displaywith high contrast, and the display by illumination of backlight is notinverted, thereby indicating a single colored display in a metallic tonewith high visibility even at night.

Modification of Third Embodiment

Although the 240° twist-aligned STN liquid crystal cell was employed asthe STN liquid crystal cell 14 in the third embodiment, the liquidcrystal display device which is the same as that in the third embodimentcan be obtained even if a 180° to 270° twist-aligned STN liquid crystalcell is employed.

Further, although the retardation film 9 for circularly polarized lightis installed between the second polarizing film 18 and the cholestericliquid crystal polymer sheet 10 in the third embodiment, even if theretardation film 9 for circularly polarized light is omitted, the liquidcrystal display device is feasible while the reflecting efficiency ofthe cholesteric liquid crystal polymer sheet 10 is somewhat lowered andmetallic color becomes somewhat dark.

Fourth Embodiment: FIG. 7

A liquid crystal display device according to a fourth embodiment of theinvention is now described with reference to FIG. 7.

Since the liquid crystal display device of this embodiment is the sameas the second embodiment in construction except that the translucentlight absorbing member 15 is removed, the different point alone isdescribed hereinafter.

A liquid crystal display device 40 in the fourth embodiment comprises anSTN liquid crystal cell 12 with about 225° twisted nematic liquidcrystals 6 sealed therein, a retardation film 13 and a first polarizingfilm 17 disposed successively on a visible side (upper side in FIG. 7),and a second polarizing film 18, a retardation film 9 for circularlypolarized light, a cholesteric liquid crystal polymer sheet 10 and abacklight 16 disposed successively on a side opposite from the visibleside (lower side in FIG. 7).

The backlight 16 has a function of scattering polarized light at itslight emitting surface, namely, a surface opposite to the cholestericliquid crystal polymer sheet 10.

The operation for displaying colors by the liquid crystal display device40 in the fourth embodiment is described next. In a state where novoltage is applied to the STN liquid crystal cell 12 in the liquidcrystal display device 40, a linearly polarized light which falls on theretardation film 13 from the visible side through the first polarizingfilm 17 is turned in a state of an elliptic polarized light when itpasses through the retardation film 13. The elliptic polarized light iscorrected during passage through the STN liquid crystal cell 12, isturned into substantially linearly polarized light, and outgoes having apolarizing direction rotated counterclockwise by about 55° with respectto the transmission axis 17 a of the first polarizing film 17 shown inFIG. 4.

Since the second polarizing film 18 is disposed so that a transmissionaxis 18 a of the second polarizing film 18 is oriented in the directionof −15° on the basis of a horizontal axis H, the linearly polarizedlight falling thereon from the first polarizing film 17 passes thesecond polarizing film 18 as it is.

Since the retardation film 9 for circularly polarized light is disposedat the angle of +45° with respect to the second polarizing film 18, thelinearly polarized light passed through the second polarizing film 18falls so that polarization thereof is at a 45° clockwise angle withrespect to a phase delay axis 9 a of the retardation film 9 forcircularly polarized light, and it is turned into a right-handedcircularly polarized light.

Since the fourth embodiment employed the cholesteric liquid crystalpolymer sheet 10 which is twisted right in the same manner as the firstembodiment, light components in a scattering band width Δλ is reflectedaround a scattering center wavelength λc are reflected due to theselective scattering phenomenon.

Transmitted light other than light components in the scattering bandwidth Δλ reaches the backlight 16 because the translucent lightabsorbing member 15 provided in the second embodiment is not provided inthe fourth embodiment. An EL plate showing emitted light in a bluishgreen is employed as the backlight 16 in the same manner as the secondembodiment. The EL plate is prepared by printing granular light emittingbodies on a base film, then covering the base film with a film forming atransparent electrode thereon. Accordingly, the light emitting surfaceof the EL plate has a function of scattering polarized light so thattransmitted light other than the light components in the scattering bandwidth Δλ and reached the backlight 16 is disturbed its polarized stateby the granular light emitting bodies, and hence it is reflected.

In FIG. 7, the reflected light from the backlight 16 transmits throughthe cholesteric liquid crystal polymer sheet 10, then transmits throughthe retardation film 9 for circularly polarized light again and reachesthe second polarizing film 18. However, a state of polarization isdisturbed by the backlight 16, the light can not be returned to acomplete linearly polarized light by the retardation film 9 forcircularly polarized light, and hence the reflected light from thebacklight 16 is almost absorbed by the second polarizing film 18.Accordingly, it is possible to obtain a reflected gold color in a brightmetallic tone even if the translucent light absorbing member 15 isomitted.

When a voltage is applied between first transparent electrodes 3 of theSTN liquid crystal cell 12 and second transparent electrodes 4 thereof,the molecules in the nematic liquid crystals 6 are caused to rise up,and birefringency of the STN liquid crystal cell 12 undergoes a change,so that polarization direction of the linearly polarized outgoing lightis rotated by about 90° so as to be in the direction at +75° withrespect to the horizontal axis H. Accordingly, since the polarizationdirection of the linearly polarized light transmitted through the STNliquid crystal cell 12 is deviated by 90° from the transmission axis 18a of the second polarizing film 18, so that all components of lightfalling on the second polarizing film 18 are absorbed thereby,indicating black display.

Since the liquid crystal display device employs the EL plate having aluminescence center wavelength of λL=510 nm, and showing emitted lightin a bluish green color as the backlight 16 in the same manner as thefirst embodiment, the light can not be transmitted in a black displaystate where no voltage is applied, while light in wavelength of not morethan 560 nm can be transmitted in a state where golden reflected coloris displayed when no voltage is applied, so that a brightness relationis indicated in the same way as the display by external light, and hencean excellent visibility can be obtained.

Since the translucent light absorbing member is not provided in theliquid crystal display device of the fourth embodiment compared with thesecond embodiment, the amount of transmitted light increases when thebacklight is lit up to increase display brightness, so that brightillumination can be obtained.

As mentioned above, with the construction comprising the liquid crystaldisplay device comprising the first polarizing film 17, the retardationfilm 13, the STN liquid crystal cell 12, the second polarizing film 18,the retardation film 9 for circularly polarized light, the cholestericliquid crystal polymer sheet 10 and the backlight 16, it is possible toobtain a liquid crystal display device capable of indicating brightreflected color with high contrast, and indicating the same display inbrightness relation between illumination by backlighting and the displayby an external light, and indicating a single color display in highmetallic tone to enhance high visibility even at night.

Modification of Fourth Embodiment

Although the STN liquid crystal cell 12 and the retardation film 13 areemployed in the fourth embodiment, the function of scattering polarizedlight on the light emitting surface of the backlight 16 may be utilizedwhile removing the translucent light absorbing member 15 in the samemanner as the liquid crystal display device of the fourth embodimenteven in the liquid crystal display device employing the TN liquidcrystal cell 7 used in the first embodiment, or in the liquid crystaldisplay device employing the STN liquid crystal cell 14 and the twistedphase difference plate 19 used in the third embodiment. Even in suchcases, a bright display can be obtained when the backlight is lit up,compared with the liquid crystal display devices in the first and thirdembodiment.

Further, although the EL plate showing emitted light in a bluish greencolor is used as the backlight 16 in the fourth embodiment, it ispossible to use a side light provided with a light emitting diodeshowing emitted light in a green color which is attached to a plasticlight guide plate. In this case, an effective function of scatteringpolarized light can be obtained by providing irregularities on thesurface of the plastic light guide plate, a reflector having a roughsurface at the lower portion of the plastic light guide, or the like.

Fifth Embodiment: FIG. 8

A liquid crystal display device according to a fifth embodiment of theinvention is now described with reference to FIG. 8.

Since the liquid crystal display device of this embodiment is the sameas the second embodiment in construction as explained with reference toFIGS. 3 and 4 except that the second polarizing film is areflection-type polarizing film, the different point alone is describedhereinafter with reference to FIG. 8.

A liquid crystal display device 40 in the fourth embodiment comprises anSTN liquid crystal cell 12 with about 225° twisted nematic liquidcrystal sealed therein, a retardation film 13, and a first polarizingfilm 17 disposed successively on a visible side (upper side in FIG. 8),and a reflective polarizing film 26, a retardation film 9 for circularlypolarized light, a cholesteric liquid crystal polymer sheet 10,translucent light absorbing member 15 and a backlight 16 disposedsuccessively on a side opposite from the visible side (lower side inFIG. 8).

The reflection-type polarizing film 26 is first described. The firstpolarizing film 17 and the second polarizing film 18 which have beenemployed in the first to fourth embodiments are formed of normalpolarizing films, namely, absorption-type polarizing films which absorblinearly polarized light having polarizing direction which intersects atransmission axis at right angle, and indicates a black display. On theother hand, the reflection-type polarizing film reflects linearlypolarized light having polarizing direction which intersects atransmission axis at right angle, and indicates a silver display. In thefifth embodiment, a product called as D-BEF manufactured by Sumitomo 3Mcorporation is used as a reflection-type polarizing film.

The operation for displaying colors by the liquid crystal display device40 in the fifth embodiment is described next. In a state where novoltage is applied to the STN liquid crystal cell 12 in the liquidcrystal display device 40, a linearly polarized light which falls on theretardation film 13 from the visible side through the first polarizingfilm 17 is turned in a state of an elliptic polarized light when itpasses through the retardation film 13. The elliptic polarized light iscorrected during passage through the STN liquid crystal cell 12, isturned into substantially linearly polarized light, and outgoes having apolarization direction rotated counterclockwise by about 55° withrespect to the transmission axis 17 a of the first polarizing film 17shown in FIG. 4.

Since the transmission axis of the reflection-type polarizing film 26 isthe same of the transmission axis 18 a of the second polarizing film 18in the second embodiment and is disposed so that it is oriented in thedirection of 15° on the basis of a horizontal axis H. Accordingly, thelinearly polarized light which falls on from the first polarizing film17 passes through the reflection-type polarizing film 26 as it is.

Since a phase delay axis 9 a of the retardation film 9 for circularlypolarized light is disposed at an angle of +45° relative to atransmission axis of the reflection-type polarizing film 26, thelinearly polarized light which passed through the reflection-typepolarizing film 26 falls at a 45° clockwise angle with respect to aphase delay axis 9 a of the retardation film 9 for circularly polarizedlight and it is turned into right-handed circularly polarized light.

Since the fifth embodiment employed the cholesteric liquid crystalpolymer sheet 10 which is twisted right in the same manner as the firstembodiment, light components in a scattering band width Δλ is reflectedaround a scattering center wavelength λc are reflected due to theselective scattering phenomenon, and light transmitted throughwavelength regions other than the scattering bandwidth Δλ, is absorbedby the translucent light absorbing member 15, whereupon a goldenreflected color in a bright metallic tone can be obtained.

When a voltage is applied between first transparent electrodes 3 of theSTN liquid crystal cell 12 and second transparent electrodes 4 thereof,the molecules in the nematic liquid crystals 6 are caused to rise up,and birefringency of the STN liquid crystal cell 12 undergoes a change,so that polarization of the linearly polarized light outgoing is rotatedby about 90° so as to be in the direction at +75° with respect to thehorizontal axis H. Accordingly, since polarization direction of thelinearly polarized light transmitted through the STN liquid crystal cell12 is deviated by 90° from the transmission axis of the secondpolarizing film 26, so that almost all components of light falling onthe second polarizing film 26 are reflected thereby, indicating silverdisplay.

Since the liquid crystal display device employs the EL plate having aluminescence center wavelength of λL=510 nm, and showing emitted lightin a bluish green color as the backlight 16 in the same manner as thefirst embodiment, the light can not be transmitted in a silver displaystate where a voltage is applied, while light in a wavelength of notmore than 560 nm can be transmitted in a state where a golden reflectedcolor is displayed when no voltage is applied, and further the samedisplay in brightness relation between the display therein and thedisplay by an external light without lighting up the backlight can beobtained, to enhance high visibility even at night.

As mentioned above, with the construction comprising the liquid crystaldisplay device comprising the first polarizing film 17, the retardationfilm 13, the STN liquid crystal cell 12, the reflection-type polarizingfilm 26, the retardation film 9 for circularly polarized light, thecholesteric liquid crystal polymer sheet 10, the translucent lightabsorbing member 15 and the backlight 16, it is possible to obtain aliquid crystal display device capable of indicating silver charactersagainst background in gold with bright reflected color, which becomes acorrect conversion display in the same manner as the display by anexternal light even illumination by backlighting, and of indicating asingle colored display in a metallic tone with high visibility even atnight.

Modification of Fifth Embodiment

Although the STN liquid crystal cell 12 and the retardation film 13 areemployed in the fifth embodiment, if a reflection-type polarizing film26 is employed in place of a second polarizing film 18 even in theliquid crystal display device employing the TN liquid crystal cell 7 inthe first embodiment, and the liquid crystal display device employingthe STN liquid crystal cell 14 and twisted retardation film 19 in thethird embodiment, the same liquid crystal display device as the fifthembodiment can be obtained.

Further, although the liquid crystal display device displays a silvercharacter against a background in gold in this embodiment, it ispossible to display a golden character against a background in silver bytwisting a transmission axis 17 a of a first polarizing film 17 by 90°.Further, it is also possible to obtain a liquid crystal display devicecapable of displaying a variety of colors such as blue characters in ametallic tone against a background in silver, green character in ametallic tone against a background in silver by changing twist pitch ofa cholesteric liquid crystal polymer sheet 10.

Still further, although a translucent light absorbing member 15 wasprovided between the backlight 16 and the cholesteric liquid crystalpolymer sheet 10 in this embodiment, even if function of scatteringpolarized light of the light emitting surface of the backlight 16 isutilized while removing the translucent light absorbing member 15 asmentioned in the fourth embodiment, the same liquid crystal displaydevice as the fourth embodiment can be obtained.

Sixth Embodiment: FIG. 9, FIG. 10

A liquid crystal display device according to a sixth embodiment of theinvention is now described with reference to FIG. 9 and FIG. 10.

Since the liquid crystal display device of this embodiment is the sameas the first embodiment in construction except that two piecesretardation films for circularly polarized light are employed and theposition of a second polarizing film 18 is different, the differentpoints alone are described hereinafter.

The liquid crystal display device 40 comprises, as shown in FIG. 9, afirst polarizing film 17, a TN liquid crystal cell 7, a cholestericliquid crystal polymer sheet 10, a second polarizing film 18, atranslucent light absorbing member 15 and a backlight 16 disposedsuccessively on the visible side (upper side in FIG. 9), which are thesame as the first embodiment.

A first retardation film 27 for circularly polarized light disposedbetween the TN liquid crystal cell 7 and the cholesteric liquid crystalpolymer sheet 10, and a second retardation film 28 for circularlypolarized light 28 disposed between the cholesteric liquid crystalpolymer sheet 10 and the second polarizing film 18 are respectivelycalled as a quarter-wavelength plate which is the same as theretardation film 9 for circularly polarized light (FIG. 1) as employedin the first embodiment, and which is prepared by spreading apolycarbonate resin to a thickness of about 60 μm, and the phasedifference value is 140 nm.

A first substrate 1, the first retardation film 27 for circularlypolarized light, the cholesteric liquid crystal polymer sheet 10, thesecond retardation film 28 for circularly polarized light and the secondpolarizing film 18 are respectively bonded using an acrylic adhesive(not shown). Further, the first polarizing film 17 and a secondsubstrate 2 are also bonded to each other using an acrylic adhesive (notshown).

Shown in FIG. 10, the transmission axis 17 a of the first polarizingfilm 17 points 45° upward to the right in the same manner as alignmentdirection 7 b of the upper liquid crystal molecules of the TN liquidcrystal cell 7, and a transmission axis 18 a of the second polarizingfilm 18 points 45° upward to the right in the same manner as analignment direction 7 b of the upper liquid crystal molecules of the TNliquid crystal cell 7, while a phase delay axis 27 a of the firstretardation film 27 for circularly polarized light and a phase delayaxis 28 a of the second retardation film 28 for circularly polarizedlight are respectively disposed horizontally.

The operation for displaying colors by the liquid crystal display device40 of the sixth embodiment is described next.

In a state where no voltage is applied to the TN liquid crystal cell 7in the liquid crystal display device 40, a linearly polarized lightwhich is changed to the direction of the transmission axis 17 a andwhich falls thereon from a visible side through the first polarizingfilm 17 is polarized in the direction same as alignment direction 7 b ofthe upper liquid crystal molecules of the TN liquid crystal cell 7 andfalls thereon, and is rotated by 90° by the TN liquid crystal cell 7 andit outgoes after it is turned into a linearly polarized light in thealignment direction 7 a of the lower liquid crystal molecules.

The linearly polarized light outgoing from the TN liquid crystal cell 7falls on the phase delay axis 27 a of the first retardation film 27 forcircularly polarized light as a 45° right-handed linearly polarizedlight. Accordingly, as shown in the OFF-state in FIG. 13, the lightfalls thereon is turned into a right-handed circularly polarized light,and it is rotated clockwise same as the twisting direction 10 a of thecholesteric liquid crystal polymer sheet 10, so that light components ina scattering band width Δλ is reflected around a scattering centerwavelength λc are reflected due to the selective scattering phenomenon.Further, transmitted light in wavelength regions other than thescattering bandwidth Δλ transmits through the second retardation film 28for circularly polarized light, but it is absorbed by the translucentlight absorbing member 15, whereupon a golden reflected color in abright metallic tone is obtained.

If the voltage is applied between first transparent electrodes 3 andsecond transparent electrodes 4, molecules of a nematic liquid crystalsnematic liquid crystals 6 are caused to rise up to extinguish the lightrotation property so that linearly polarized light falling thereon fromthe alignment direction 7 b of the upper liquid crystal moleculestransmits through the TN liquid crystal cell 7 in the same direction asit is. Accordingly, the linearly polarized light transmitted through theTN liquid crystal cell 7 falls on the first retardation film 27 forcircularly polarized light at a 45° counterclockwise angle, so that itis turned into a left-handed circularly polarized light shown in theON-state in FIG. 13. Further, the linearly polarized light is oppositeto the twisting direction 10 a of the cholesteric liquid crystal polymersheet 10, so that light having all the wavelengths transmits through thecholesteric liquid crystal polymer sheet 10.

Light which transmitted through the cholesteric liquid crystal polymersheet 10 is returned to linearly polarized light at the secondretardation film 28 for circularly polarized light but the oscillationdirection thereof is rotated by 90° from the direction in which lightfalls on the first retardation film 27 for circularly polarized light,and becomes the same direction as an alignment direction 7 a of thelower liquid crystal molecules. Since the transmission axis 18 a of thesecond polarizing film 18 is disposed at +45° which is the same as thealignment direction 7 b of the upper liquid crystal molecules, lighttransmitted through the second retardation film 28 for circularlypolarized light is absorbed by the second polarizing film 18 to indicatea black display.

An EL plate having a luminescence center wavelength λL of 510 nm, andshowing emitted light in a bluish green color is employed as a backlight16 in the same manner as the first embodiment. When the backlight 16 islit up in a black display state where a voltage is applied, lighttransmitted through the second polarizing film 18 is rotated by 90° bythe second retardation film 28 for circularly polarized light and thefirst retardation film 27 for circularly polarized light, and it isabsorbed by the first polarizing film 17, and hence it does not transmitthrough light of the backlight 16.

In an OFF-state displaying golden reflected color when no voltage isapplied, light in a wavelength of not more than 560 nm can transmit sothat it is well illuminated, and the same display in brightness relationbetween the display therein and the display by an external light withoutlighting up by the backlight 16 (correct conversion display) to enhancea good visibility even at night.

Accordingly, with the construction comprising the first polarizing film17, the TN liquid crystal cell 7, the first retardation film 27 forcircularly polarized light, the cholesteric liquid crystal polymer sheet10, the second retardation film 28 for circularly polarized light, thesecond polarizing film 18, the translucent light absorbing member 15 andthe backlight 16, it is possible to obtain a liquid crystal displaydevice capable of indicating bright reflected color display with highcontrast, and indicating the same display in brightness relation betweenillumination by backlighting and the display by an external light, andindicating a single colored display in a metallic tone with highvisibility even at night.

Modification of the Sixth Embodiment

Although the TN liquid crystal cell 7 is employed in the sixthembodiment, even if the first retardation film 27 for circularlypolarized light, the cholesteric liquid crystal polymer sheet 10, thesecond retardation film 28 for circularly polarized light and the secondpolarizing film 18 are employed in the liquid crystal display deviceemploying the STN liquid crystal cell 12 and the retardation film 13used in the second embodiment, or in the liquid crystal display deviceemploying an STN liquid crystal cell 20, the twisted retardation film 19used in the third embodiment, the liquid crystal display device which isthe same as the sixth embodiment can be obtained.

Further, in this modification, although the translucent light absorbingmember 15 is disposed between the backlight 16 and the second polarizingfilm 18, the liquid crystal display device similar to the sixthembodiment obtained even if the translucent light absorbing member 15 isremoved as explained in the fourth embodiment.

Still further, although a normal absorption-type polarizing film isemployed as the second polarizing film 18, a reflection-type polarizingfilm can be employed as explained in the polarizing film 18, areflection-type polarizing film can be employed as explained in thefifth embodiment.

Seventh Embodiment: FIG. 12

A liquid crystal display device according to a seventh embodiment of theinvention is now described with reference to FIG. 12.

Since the liquid crystal display device of the seventh embodiment is thesame as the second embodiment in construction as explained in FIG. 3except that an EL plate showing emitted light in a while color isemployed as a backlight, the explanation of the construction thereofusing the sectional view is omitted.

The EL plate showing emitted light in a while color is prepared bycoating fluorescent dye having light emitting wavelength of 580 nm onthe surface of the EL plate showing emitted light in a bluish greencolor employed in the second embodiment. A light emitting spectrum ofthe EL plate showing emitted light in a while color and transmittancecurve of the liquid crystal display device are shown in FIG. 12.

The light emitting operation and the operation when the backlight is litup in the seventh embodiment of the invention are now described withreference to FIG. 12.

In FIG. 12, the transmittance of the liquid crystal display device in astate where no voltage is applied to the liquid crystal display devicein the seventh embodiment at the selective scattering state is shown bya solid curve 53, whereas the transmittance of the same in a state whereno voltage is applied to the liquid crystal display device at the blackdisplay state is shown by a solid curve 52. In a state where no voltageis applied, it is found from the curve 53 that right-handed circularlypolarized light in the range from 560 nm to 670 nm around the scatteringcenter wavelength of λc=610 nm is reflected, but light components inwavelength regions other than the scattering bandwidth transmit as theyare.

Accordingly, if the transmitted light is absorbed by the translucentlight absorbing member 15 or the returning of light to the visible sideis restrained by the function of scattering polarized light on the lightemitting surface of the backlight 16, it is possible to indicate abright golden display by the reflected light due to the selectivescattering phenomenon.

On the other hand, in a state where a voltage is applied, it is foundfrom the curve 52 that light transmitted through the first polarizingfilm 17 is almost absorbed by the second polarizing film 18 to indicatea black display.

The operation of the backlight 16 is described next. Since the EL plateshowing emitted light in a while color is prepared by printingfluorescent dye having luminescence center wavelength of 580 nm on thesurface of the EL plate showing emitted light in a bluish green color,it has two luminescence center wavelengths. A curve 55 denoted by brokenline in FIG. 12 shows a relative light emitting spectrum of the EL plateshowing emitted light in a while color used in the seventh embodiment.The EL plate showing emitted light in a while color has two lightluminescence peaks, i.e., a first luminescence center wavelength λL1=490nm and a second luminescence center wavelength λL2=580 nm, and it showswhitish light emitting color.

Although the liquid crystal display device indicates a golden reflectedcolor display in a state where no voltage is applied, light having awavelength of not more than 560 nm can transmit through the cholestericliquid crystal polymer sheet 10. Accordingly, light having the firstlight luminescence peak, and light having the wavelength which isshorter than the second luminescence center wavelength λL2 of the secondlight luminescence peak respectively transmit through the cholestericliquid crystal polymer sheet 10 and can brightly illuminate so that ahigh visibility can be obtained even at night.

By the employment of not less than two luminescence center wavelengthsas the backlight 16 as described above, it is possible to indicate abright reflected color display with high contrast and to indicate thesame display in brightness relation between the display therein and thedisplay by an external light without illumination by backlighting, thusindicating a single colored display in a metallic tone with a highvisibility even at night.

Modification of Seventh Embodiment

Although the STN liquid crystal cell 12 and the retardation film 13 areemployed in the seventh embodiment, if the EL plate showing emittedlight in a while color having a plurality of luminescence centerwavelengths as the back light 16 is employed even in the liquid crystaldisplay device employing the TN liquid crystal cell 7 used in the firstembodiment, or in the liquid crystal display device employing the STNliquid crystal cell 20 and the twisted retardation film 19 used in thethird embodiment, the liquid crystal display device which is the same asthe seventh embodiment can be obtained.

Although the EL plate showing emitted light in a while color is preparedby coating florescent dye having light emitting wavelength 580 nm on thesurface of an EL plate showing emitted light in a bluish green color inthe seventh embodiment, it is possible to employ the EL plate showingemitted light in a while color prepared by printing florescent dye onthe lower side of a transparent electrode on the surface of the EL plateshowing emitted light in a bluish green color or by mixing florescentdye into bluish green light emitting body.

Further, although an EL plate having two luminescence centerwavelengths, namely, the luminescence center wavelengths λL1=490 nm andλL2=580 nm has been used as the backlight 16 in the seventh embodiment,if at least one light emitting wavelength is deviated from the selectivescattering center wavelength λc of the cholesteric liquid crystalpolymer sheet 10 by not less than 50 nm, bright display can be obtainedwhen the EL plate is lit up.

Still further, although an EL film showing emitted light in a whitecolor is used as the backlight 16 in the seventh embodiment, even if aside light provided with two kinds of, i.e., green and red lightemitting diodes in light emitting color which are attached to a plasticlight guide plate, or a side light provided with white florescent lightin light emitting color which is attached to a plastic light guide plateis used in this embodiment, the same bright illumination can beobtained.

Still further, although the translucent light absorbing member 15 isprovided between the backlight 16 and the cholesteric liquid crystalpolymer sheet 10 in the seventh embodiment, it is needless to say thatthe same liquid crystal display device as the seventh embodiment can beobtained even if the translucent light absorbing member 15 is removed asexplained in the fourth embodiment.

Industrial Applicability

As is evident from the above explanation, it is possible to obtain theliquid crystal display device capable of indicating a single reflectedcolor display in a bright metallic tone, and capable of displaying asingle color which can be visible even at dark environment such as nightby lighting up the backlight.

Further, if the liquid crystal display device does not employ atranslucent light absorbing member, it is possible to indicate a singlecolor display in a bright metallic tone to obtain more bright reflectedcolor, and also capable of increasing brightness when the backlight islit up.

Accordingly, the liquid crystal display device according to theinvention can be expected to be utilized in a broad area as displaydevices, of the variety of watches, portable electronic devices, gamedevices, or the like.

What is claimed is:
 1. A liquid crystal display device comprising: a TNliquid crystal cell with about 90° twisted nematic liquid crystalssealed in-between a pair of transparent substrates having respectivetransparent electrodes; a first polarizing film disposed on a visibleside of the TN liquid crystal cell; and a second polarizing film, aretardation film for circularly polarized light, a cholestric liquidcrystal polymer sheet, a translucent light absorbing member and abacklight disposed successively on a side of the TN liquid crystal cell,opposite from the visible side thereof.
 2. A liquid crystal displaydevice comprising: an STN liquid crystal cell with 180° to 270° twistednematic liquid crystals sandwiched between a pair of transparentsubstrates having respective transparent electrodes; a retardation filmdisposed on a visible side of the STN liquid crystal cell; a firstpolarizing film disposed on an outer side of the retardation film; and asecond polarizing film, a retardation film for circularly polarizedlight, a cholestric liquid crystal polymer sheet, a translucent lightabsorbing member and a backlight disposed successively on a side of theSTN liquid crystal cell, opposite from the visible side thereof.
 3. Aliquid crystal display device according to claim 2, wherein theretardation film is a twisted retardation film.
 4. A liquid cell displaydevice comprising: a TN liquid crystal cell with about 90° twistednematic liquid crystals sealed in-between a pair of transparentsubstrates having respective electrodes; a first polarizing filmdisposed on a visible side of the TN liquid crystal cell; and a secondpolarizing film, a retardation film for circularly polarized light, acholestric liquid crystal polymer sheet and a backlight disposedsuccessively on a side of the TN liquid crystal cell, opposite from thevisible side thereof, wherein a face of said backlight, opposite to saidcholestric liquid crystal polymer sheet, has a function of scatteringpolarized light.
 5. A liquid crystal display device comprising: an STNliquid crystal cell with 180° to 270° twisted nematic liquid crystalssandwiched between a pair of transparent substrates having respectivetransparent electrodes; a retardation film disposed on a visible side ofthe STN liquid crystal cell; a first polarizing film disposed on anouter side of the retardation film; and a second polarizing film, aretardation film for circularly polarized light, a cholestric liquidcrystal polymer sheet and a backlight disposed successively on a side ofthe STN liquid crystal cell, opposite from the visible side thereof,wherein a face of said backlight, opposite to said cholestric liquidcrystal polymer sheet, has a function of scattering polarized light. 6.A liquid crystal display device according to claim 5, wherein theretardation film is a twisted retardation film.
 7. A liquid crystaldisplay device comprising: a TN liquid crystal cell with about 90°twisted nematic liquid crystals sealed in-between a pair of transparentsubstrates having respective transparent electrodes; a first polarizingfilm disposed on a visible side of the TN liquid crystal cell; and afirst retardation film for circularly polarized light, a cholestricliquid crystal polymer sheet, a second retardation film for circularlypolarized light, a second polarizing film, a translucent light absorbingmember and a backlight disposed successively on a side of the TN liquidcrystal cell, opposite from the visible side thereof.
 8. A liquidcrystal display device comprising: an STN liquid crystal cell with 180°to 270° twisted nematic liquid crystals sandwiched between a pair oftransparent substrates having respective transparent electrodes; aretardation film disposed on a visible side of the STN liquid crystalcell; a first polarizing film disposed on an outer side of theretardation film; and a first retardation film for circularly polarizedlight, a cholestric liquid crystal polymer sheet, a second retardationfilm for circularly polarized light, a second polarizing film, atranslucent light absorbing member and a backlight disposed successivelyon a side of the STN liquid crystal cell, opposite from the visible sidethereof.
 9. A liquid crystal display device according to claim 8,wherein the retardation film is a twisted retardation film.
 10. A liquidcrystal display comprising: a TN liquid crystal cell with about 90°twisted nematic liquid crystals sealed in-between a pair of transparentsubstrates having respective transparent electrodes; a first polarizingfilm disposed on a visible side of the TN liquid crystal cell; and afirst retardation film for circularly polarized light, a cholestricliquid crystal polymer sheet, a second retardation film for circularlypolarized light, a second polarizing film and a backlight disposedsuccessively on a side of the TN liquid crystal cell, opposite from thevisible side thereof, wherein a face of said backlight, opposite to saidsecond polarizing film, has a function of scattering polarized light.11. A liquid crystal display device comprising: an STN liquid crystalcell with 180° and 270° twisted nematic liquid crystals sandwichedbetween a pair of transparent substrates having respective transparentelectrodes; a retardation film disposed on a visible side of the STNliquid crystal cell; a first polarizing film disposed on an outer sideof the retardation film; and a first retardation film for circularlypolarized light, a cholestric liquid crystal polymer sheet, a secondretardation film for circularly polarized light, a second polarizingfilm and a backlight disposed successively on a side of the STN liquidcrystal cell, opposite from the visible side thereof, wherein a face ofsaid backlight, opposite to said second polarizing film, has a functionof scattering polarized light.
 12. A liquid crystal display deviceaccording to claim 11, wherein the retardation film is a twistedretardation film.
 13. A liquid crystal display device according to claim1, wherein a luminescence center wavelength of the backlight is deviatedby not less than 50 nm from a selected scattering center wavelength ofthe cholestric liquid crystal polymer sheet.
 14. A liquid crystaldisplay device according to claim 4, wherein a luminescence centerwavelength of the backlight is deviated by not less than 50 nm from aselected scattering center wavelength of the cholestric liquid crystalpolymer sheet.
 15. A liquid crystal display device according to claim 7,wherein a luminescence center wavelength of the backlight is deviated bynot less than 50 nm from a selected scattering center wavelength of thecholestric liquid crystal polymer sheet.
 16. A liquid crystal displaydevice according to claim 10, wherein a luminescence center wavelengthof the backlight is deviated by not less than 50 nm from a selectedscattering center wavelength of the cholestric liquid crystal polymersheet.
 17. A liquid crystal display device according to claim 1, whereinthe backlight has not less than two luminescence center wavelengths, andat least one of the luminescence center wavelengths is deviated by notless than 50 nm from a selected scattering center wavelength of thecholestric liquid crystal polymer sheet.
 18. A liquid crystal displaydevice according to claim 4, wherein the backlight has not less than twoluminescence center wavelengths, and at least one of the luminescencecenter wavelengths is deviated by not less than 50 nm from a selectedscattering center wavelength of the cholestric liquid crystal polymersheet.
 19. A liquid crystal display device according to claim 7, whereinthe backlight has not less than two luminescence center wavelengths, andat least one of the luminescence center wavelengths is deviated by notless than 50 nm from a selected scattering center wavelength of thecholestric liquid crystal polymer sheet.
 20. A liquid crystal displaydevice according to claim 10, wherein the backlight has not less thantwo luminescence center wavelengths, and at least one of theluminescence center wavelengths is deviated by not less than 50 nm froma selected scattering center wavelength of the cholestric liquid crystalpolymer sheet.
 21. A liquid crystal display device according to claim 1,wherein the second polarizing film is a reflection-type polarizing film.22. A liquid crystal display device according to claim 4, wherein thesecond polarizing film is a reflection-type polarizing film.
 23. Aliquid crystal display device according to claim 7, wherein the secondpolarizing film is a reflection-type polarizing film.
 24. A liquidcrystal display device according to claim 10, wherein the secondpolarizing film is a reflection-type polarizing film.